Re: [Haskell-cafe] Textbook example of instance Foldable ((,) a)

23 Nov 2020


      On Mon, 23 Nov 2020, Manuel Schneckenreither wrote:
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"SP" == Sven Panne  writes:
SP> Am Mo., 23. Nov. 2020 um 14:54 Uhr schrieb Johannes Waldmann
   SP> : [...] Henning already
   SP> called this "Matlab league" behaviour,
   SP> https://mail.haskell.org/pipermail/libraries/2016-February/026678.html
What is the intiutive way of implementing the tuple instance like this [1]
instance Foldable ((,) a) where
     ..
     length _ = 1
     ..
I cannot come up with a real argument, except to say there is something.
"length (a,b) == 1" is only a consequence of defining instance Foldable 
for pairs. It was not the argument to implement that instance, at all.

Re: [Haskell-cafe] Textbook example of instance Foldable ((,) a)

Henning Thielemann